Packing for heat-and material-exchange columns

ABSTRACT

The invention relates to a packing for heat- and material-exchange columns, with a number of approximately perpendicularly arranged corrugated plates (or strips), with the side surfaces thereof lying adjacent to each other. The ribs of the above lie very close to each other and run from top to bottom, in the approximate form of an arc, whereby the ribs of two adjacent plates cross each other and the ribs in the upper region of a plate are straight and inclined to the upper, in particular, horizontal plate edge and, in the lower region of the plate, run bent in the form of an arc.

[0001] The invention relates to a packing for heat exchange and materialexchange [mass transfer] columns with a multiplicity of generallyvertically arranged corrugated plates (or strips) having their sidesurfaces adjacent one another and whose adjacent ribs run from top tobottom in a generally arcuate pattern whereby the ribs of two adjoiningplates cross each other.

[0002] In distillation, absorption, gas scrubbing and similar operationsin process technology, columns are used which contain baffles for theheat exchange and mass transfer exchange between liquid and gas. Thesebaffles are comprised either of trays, for example bubble trays, tunneltrays, sieve trays or valve trays, of randomly arranged packings likefor example Raschig rings, Pall rings or saddles, or of ordered packingsin various geometric configurations.

[0003] With ordered packings the geometries of cross channel structureshave ranged widely in technological applications. As is generally thecase with packed columns, maximum capacity with ordered packing is alsolimited in the cross-channel structure by the development of a floodedstate. The visual observation of the flooded state in distillationcolumns which are equipped with packings of a cross channel structurewhich shows that the flooding always develops at the lower edge of theindividual packing layers. In order to increase productivity of suchpackings, one seeks to modify the lower edge of the individual packinglayers and partly in addition the upper edge of the individual packinglayers so at to increase the attainable throughput of liquid and gas.

[0004] In EP 858 830 A1 it is proposed to increase the spacing ofneighboring packing elements at the lower edge of the packing layers bythere reducing the bend height. As a further possibility a partial orcomplete removal of a part of the material, for example at every secondpacking element from the lower end of the packing layer. The drawback ofthis approach is that it affects the separating efficiency and causesdeterioration in the mechanical strength of the packing.

[0005] The alternative possibility is protected in WO 97/16247 in whichthe geometry of the cross-channel structure is altered. The bends are noloner straight as is customarily the case, but rather are of S shapeconfiguration and are so arranged that the short column orientation atthe lower and upper ends of the packing layers run approximatelyvertically. The fabrication of this packing is expensive. A drawback isthat over the packing height there are small lateral offsets of the flowpassages through the vertically-running lower and upper ends. Thisreduces the desired lateral transverse mixing of the gas flow. Tocompensate for this drawback, additional liquid collectors anddistributors must be optionally provided to limit the problematicaldistributions.

[0006] DE 39 18 483 describes a packing with a variable height geometryin which the short columns of the cross-channel structure runsubstantially vertically and parallel to one another at the lower endand are increasingly bent toward the horizontal upwardly. In order toprovide at the lower region of the packing layer, a sufficientmechanical stability in the bends between neighboring corrugations orfolds, planar sections are provided. Here as well a damming up of liquidshould be avoided.

[0007] A packing with a cross-channel structure is described in DE 29 21270 C2 in which the folds have an arcuate path. The individual platesare alternatively so mounted that the greater flow resistance liesalternately upwardly and downwardly so that in this construction thereis no shift of the flooding state to higher loadings. Further packingswith nonlinear fold paths are described in DE 12 93 796, DE 12 87 096,FR 14 79 375 and GB 10 80 991.

[0008] The object of the invention is to provide an ordered packingwhich can have an increased throughput by comparison with the knownpacking in cross-channel structures.

[0009] This object is achieved according to the invention in that theribs in the upper region of a plate are straight and inclined to theupper, especially horizontal plate edge and in the lower region of theplate run with an arcuately curved pattern.

[0010] Such a packing produces an especially high throughput at anoptimal efficiency. The structure is simple and enables inexpensivemanufacture and simple mounting.

[0011] Advantageous embodiments of the invention are shown in thedrawings and will be described in the following in greater detail. Theyshow

[0012]FIG. 1: a perspective illustration of two adjacent plates/stripsin section whereby the upper one is removed in the region to the right,

[0013]FIGS. 2a and b: bend angles at the lower ends of a plate/strip,

[0014]FIG. 3: different cross sections of ribs each illustrated within aframe,

[0015]FIGS. 4 and 5: research results with the packing according to theinvention.

[0016] The packing is comprised of a multiplicity of strips or plates 1which lie against one another with their side surfaces, which areprovided with ribs lying transversely to the longitudinal direction,whereby the strips 1 are so arranged that the ribs of neighboring stripsin contact with one another cross each other and run in arcs 3 which areparallel to one another. The arcs at their lower portions preferablyhave an arc-segmental pattern 4 and transition in the middle region 5into linear rib segments 6 which are inclined to vertical. The ribs 2have at the upper edge 7 of the packing an angle a of 30 to 70°,preferably 45 to 60°, to the horizontal and at the lower edge 8 an angleb of 75 to 88°, preferably from 80 to 85°, whereby these inclinations ofthe ribs are in the same or in opposite directions of those at the upperends of the packing.

[0017] Alternatively to the continuous arcuate pattern of the ribs it ispossible to approximate the pattern by a multiplicity of linear segmentsor similar geometries, see FIG. 3.

[0018] Preferably, the fold angle a which the ribs 2 of the strips form,are so configured upon fabrication that they over the height of thepacking in the horizontal direction always yield cross sectional areaswith approximately square cross sections.

[0019] Thus for a given utilization of material, a packing structurewith the greatest possible hydraulic diameter is formed.

[0020] The desired square openings is achieved in the simplest manner byvariation of the band angle outlet. This varies in the case ofcommercially-available packing of a cross channel structure betweenabout 70° and 90°. Between the fold angle α the inclination angle β ofthe bends with respect to the horizontal and the angle γ which the bendsform with respect to one another in the horizontal direction, thefollowing relationship applies

tan α/2=tan γ/2·sin β.

[0021] For the preferred case of square openings with γ=90°, one obtains

tan α/2=sin β.

[0022] One thus chooses the bend angle α for example with an inclinationangle β of 45 to 79.5° and with an inclination angle β of 60 to 81.8°.

[0023] In a preferred and, not sharp-edged configuration of the fold 1,the bend radius of the fold is preferably less than 15% of the ribwidth. A sharp edged configuration should be avoided since it will favordroplet entrainment.

[0024] To avoid droplet entrainment, the angle β which the ribs 2 format the upper edge of the packing with respect to the horizontal shouldnot lie below a value of 30° to 45°, preferably 45° to 60°.

[0025] The circular arc pattern of the ribs 2 should be transmitted aswell as possible. With two sharp deflections, a stronger dropletentrainment can be observed. This is especially the case for packingswhich on the lower and upper ends of the packing layers have bends withespecially narrow radii. According to the invention the bend radius ofthe ribs should not be below 25%, preferably 30%, to the height of thepacking layer. In combination with bends which are configured withoutsharp edges, experimental tests have shown an especially effectivesuppression of the droplet entrainment.

[0026] To the planar ribs which are configured as in the state of theart, other rib forms which are variable in height or height-independentcan be used to further reduce the droplet entrainment whereby,height-dependent profiles starting from a planar form, introduce asurface enlargement which can make the heat exchange and mass transfermore effective. According to the invention, with height-dependentprofiles, the lower end has a planar form using the greatest possiblehydraulic diameter. FIG. 3 shows possible configurations from which thepreferred are nonsharp edged bent forms, especially effective are roundforms for reducing the droplet entrainment.

[0027] Neighboring packing layers are rotated with respect to oneanother respectively by 30 to 150°, preferably 90°. Upon introduction ofthe packing layers, the layers preferably are additionally dynamicallyloaded, for example by hammering or are statically loaded, for exampleby the application of weights so that the number of contact locations isincreased. The strength of these effects will depend upon the packingmaterial used.

[0028] The packing of the invention permits throughput which exceedthose of conventional packing by some 30 to 50%. FIG. 4 shows theresults of tests with the air/water system.

1. A packing for heat exchange and mass transfer columns with amultiplicity of generally vertically-arranged corrugated plates (orstrips) (1), having their side surfaces lying against one another, whoseneighboring ribs (2) are in contact and run generally arcuately fromabove to below, whereby the ribs of two adjoining plates across oneanother is characterized in that; that the longitudinal line of theupper ends of the ribs (2) form an angle (a) with the upper, especiallyhorizontal, plate edge of 30 to 70°, preferably 45 to 60°, that thelongitudinal lines of the lower end of the rib (2) form an angle (b)with the lower, especially horizontal, plate edge of 75 to 90°,preferably 80 to 85°, whereby the longitudinal line extends in the sameor opposite directions of the ribs at the upper ends.
 2. A packingaccording to claim 1, characterized in that at the crossing locationsbetween the ribs (2) of one plate (1) lying thereagainst, the ribs havea cross sectional area between them with approximately square shape. 3.A packing according to claim 1 or 2, characterized in that the ridgeextending longitudinally of a rib forms an arch whose radius is lessthan 15% of the rib width.
 4. A packing according to one of thepreceding claims, characterized in that the arc-shaped rib pattern isassembled from a multiplicity of straight segments or similar shapessegmentally.
 5. A packing according to one of the preceding claims,characterized in that the ribs (2) vary in profile and thus in theircross sectional shape over the height of the packing.
 6. A packingaccording to one of the preceding claims, characterized in that thepacking layers disposed one above the other and in contact with oneanother are each rotated with respect to the other by 30 to 150°,preferably by 90°.
 7. A packing according to one of the precedingclaims, characterized in that the layers are additionally dynamicallyloaded upon insertion.